An infrared sensor of a non-cooling type (a thermal type) is a device that has an infrared sensing unit absorbing collected infrared rays, and converts the energy of radiation into electrical signals. Such a device characteristically has the infrared ray absorber and the detector cell with a thermoelectric converting element thermally isolated from the outside environment. To realize such a structure, a surface microstructure or a bulk microstructure forming technique is required. Unlike an infrared sensor of a cooling type that is expensive and requires a large-size cooler, an infrared sensor of a non-cooling type is inexpensive and can be advantageously made smaller.
To achieve thermal isolation, it is essential to set the detector cell in a vacuum, and lower the heat conductance of the supporting structure that physically and electrically connects the detector cell and a substrate. The heat conductance of the supporting structure becomes lower, as the size of the supporting structure becomes smaller. Therefore, the sensitivity of the sensor can be made higher by relaxing the design rules in the process to form the above structure.
As a conventional art, a robust supporting leg structure is disclosed. The supporting leg structure reduces strain caused by internal stress, so as to avoid the requirement for high precision in assembling when the supporting legs are made smaller to improve the heat insulation properties of the supporting legs. Also, according to a conventional technique, a titanium or titanium nitride thin film having lower heat conductance, instead of polycrystalline Si, is used as the material of the supporting leg interconnect unit. According to a conventional technique, by arching the supporting leg structure in advance, a stable process margin is provided even where the supporting legs are made smaller and thinner.
The size of the supporting leg interconnects in a miniaturization process is defined by the mask precision when the heat conductance of the supporting legs are lowered. Therefore, it is difficult to stably reduce the size to below the defined size.